Yield Strength

Deformation Limit

Transition from elastic to plastic behavior is usually defined by a 0.2 percent offset on the stress strain curve for materials without a sharp yield point. Yield strength is influenced by the grain size and the heat treatment history of the metal. For the fasteners and terminals in a battery pack, staying below this limit is essential to maintain the contact pressure required for low electrical resistance.

If the yield strength is exceeded, the resulting permanent set can lead to loose connections and overheating.

Design Specification

Safety factors are applied to the yield strength to ensure that the actual stresses in the part remain well within the elastic range. Yield strength data informs the selection of the appropriate material grade for the crash protection frames. High yield strength allows for the use of thinner sections, which is a primary strategy for reducing the overall mass of an electric vehicle.

Engineers must account for the fact that this value can change depending on the direction of the rolling in the metal sheet.

Temperature Sensitivity

Mechanical resistance of most alloys decreases as the temperature of the battery pack increases during fast charging or high power discharge. Yield strength must be evaluated at the maximum operating temperature of the system to ensure the structure remains stable. In cold climates, some materials may show an increase in yield strength but a corresponding drop in toughness.

This relationship is managed by selecting materials that maintain a consistent performance across the full thermal range of the vehicle. Monitoring this property ensures that the battery enclosure will protect the cells from mechanical damage throughout the life of the product.